The invention relates to a method for inhibiting the carbon-carbon double bond isomerization of substituted or unsubstituted hydrocarbon compounds. In one aspect the invention relates to a method for inhibiting the carbon-carbon double bond isomerization of a mononitrile. In another aspect the invention relates to a process for producing unsaturated dinitriles employing the above-noted method for inhibiting the carbon-carbon double bond isomerization of a mononitrile.
Isomerization reactions involving the carbon-carbon double bond rearrangement of a variety of substituted or unsubstituted hydrocarbon compounds are well known in the art. Isomerization reactions are frequently employed in a process to increase the overall production of a specific compound from a multicomponent feedstream as, for example, in a process for producing 2-butene from a feedstream comprising 1-butene and 2-butene. However, there are other instances, as in the present invention, where it is desirable to inhibit an isomerization reaction. For example it is frequently desirable to store a certain compound having olefinic unsaturation in a less stable form as compared to an isomer of said compound having olefinic unsaturation in a more stable form; however, isomerization often occurs spontaneously, thus providing a mixture of isomers. Such a situation exists in the storage of 5-methyl-5-hexenenitrile, for example, of which a portion will spontaneously isomerize to produce 5-methyl-4-hexenenitrile, the more stable isomer. Likewise it is desirable to inhibit the isomerization of a compound existing in a less stable form when said compound is being used as a reactant in a reaction and an isomer of said compound having a more stable form produces an undesirable product. Such a situation can exist when an olefinically unsaturated mononitrile such as, for example, acrylonitrile, an olefinic hydrocarbon reactant such as, for example, isobutylene and the reaction product of the unsaturated mononitrile and the olefinic hydrocarbon reactant, frequently referred to as a monoadduct, such as, for example, 5-methyl-5-hexenenitrile, produced by reacting acrylonitrile and isobutylene, are reacted in the presence of an aqueous diluent to produce an olefinically unsaturated dinitrile product frequently referred to as a diadduct, such as, for example, 5-methylene-1,9-nonanedinitrile. This reaction is generally described in U.S. Pat. No. 3,985,786, issued to Charles A. Drake on Oct. 12, 1976. In the above-described reaction it is generally undesirable for the 5-methyl-5-hexenenitrile to isomerize to 5-methyl-4-hexenenitrile during the reaction. Inhibitors suitable for use in the above-described reaction are disclosed in U.S. Pat. No. 4,001,294, issued to Charles A. Drake et al on Jan. 4, 1977. As described therein as little as 0.5 weight percent of 5-methyl-4-hexenenitrile in the reaction mixture as described above will adversely affect the fiber-forming properties of polymers derived from the 5-methylene-1,9-nonanedinitrile diadduct produced by the reaction. Therefore it is clear that the use of inhibitors is of particular importance such as, for example, in the storage of certain compounds and in carrying out certain reactions, and although some such inhibitors are presently known and recognized in the art, there is still a need for additional inhibitors and inhibitors having improved inhibiting properties.
Accordingly, it is an object of the invention to inhibit the carbon-carbon double bond isomerization of a compound having olefinic unsaturation in a less stable form to a compound having olefinic unsaturation in a more stable form.
Another object of the invention is to inhibit the carbon-carbon double bond isomerization of a monoadduct produced by reacting an olefinic hydrocarbon and an olefinically unsaturated mononitrile when said monoadduct is reacted with a mononitrile to produce a dinitrile.
Another object of the invention is a carbon-carbon double bond isomerization inhibitor having little or no tendency to corrode equipment required in various processes employing said inhibitor.
Still another object of the invention is a carbon-carbon double bond isomerization inhibitor having little or no tendency to corrode equipment when employed in reactions in which an aqueous diluent is used.
Still another object of the invention is a carbon-carbon double bond isomerization inhibitor which is an effective inhibitor in concentrations substantially lower than the concentration generally required for prior art inhibitors.
These and other objects of the invention will be apparent to those skilled in the art upon studying the specification and the appended claims.
According to the invention an acyclic or an alicyclic substituted or unsubstituted hydrocarbon compound having 4 to 30 carbon atoms per molecule and having olefinic unsaturation in a less stable form is inhibited from isomerizing to produce a corresponding isomer having olefinic unsaturation in a more stable form by contacting the compound with an alkali metal salt of a di-, tri- or tetracarboxylic acid. The use of such alkali metal salts substantially precludes the carbon-carbon double bond isomerization of a wide variety of substituted and unsubstituted hydrocarbons even when employed in concentrations substantially lower than the concentrations generally required for prior art inhibitors.
Further according to the invention, the presence of an alkali metal salt of a di-, tri- or tetracarboxylic acid in a reaction mixture containing at least one olefinic hydrocarbon reactant, at least one olefinically unsaturated mononitrile reactant, at least one monoadduct reaction product of an olefinic hydrocarbon compound and an olefinically unsaturated mononitrile compound in the presence of an aqueous diluent substantially inhibits the carbon-carbon double bond isomerization of the above-described monoadduct from a less stable form with respect to the olefinic unsaturation to a more stable form. In addition it has been found that such salts are essentially noncorrosive with respect to the materials generally used in a reactor and associated equipment suitable for carrying out the above process.